The present invention relates to the field of power management systems. In particular, the present invention relates to power management systems for back-up power sources.
In the telecommunications industry, telecommunication loads are normally provided with DC power by an AC to DC converter. To ensure that telecommunication services are not interrupted when there is an AC power outage, battery strings are typically employed as back-up power sources. These battery back-up systems usually comprise multiple battery strings that are connected in parallel. In these back-up systems, each battery string is responsible for meeting a fractional portion of the load power demands.
It is often desirable to disconnect the battery string from the load, for example, for maintenance purposes or to replace the battery string. As a result, multiple battery strings may be disconnected at the same time.
There are many disadvantages, however, to allowing multiple battery strings to be simultaneously disconnected. First, if too many battery strings are disconnected at the same time, the Uninterruptable Power System (xe2x80x9cUPSxe2x80x9d) may not operate safely. When multiple battery strings are used, each battery string is responsible for meeting a fractional portion of the load current demand. In view of this, the cabling and connectors used to couple the battery strings to the power bus are selected to safely handle the expected current to be supplied by the battery strings. If multiple battery strings are disconnected from the power bus, the remaining batteries must provide increased current to meet the load demands.
For example, if the load demand is 4000 Amperes and there are 8 battery strings connected in parallel to provide power to the load during A.C. power outages, each battery string is responsible for providing 500 Amperes. If one battery string is disconnected, then the remaining batteries must now provide 571 Amperes. But if four battery strings are disconnected, the remaining batteries must provide 1000 Amperes.
The increased current levels supplied by the remaining batteries may surpass the level at which the cabling and connectors connected thereto can safely conduct current. The cabling and connectors could be sized larger to handle increased current levels, but this potential solution may needlessly increase the cost and installation complexities when in most instances the increased capacity is not be needed. Also, when multiple battery strings are simultaneously disconnected, the increased load demand on the remaining battery strings will decrease the length of time the remaining battery strings can provide power.
Therefore, there remains a need for a system that limits the number of battery strings that may be disconnected from the load to ensure that the battery back-up system can safely deliver power when needed.
The present invention meets the foregoing needs by providing a system that limits the number of battery strings that can be disconnected at a power plant at a given time.
The system groups battery strings into one or more rings wherein the number of batteries within a ring that can be disconnected is limited. One or more controllers are provided for each ring that cooperate with the other controllers within the ring to limit the number of batteries that may be disconnected from the load at a given time.
The present invention provides many advantages over the presently known power management systems. Not all of these advantages are simultaneously required to practice the invention as claimed, and the following list is merely illustrative of the types of benefits that may be provided, alone or in combination, by the present invention. These advantages include: (1) limiting the number of batteries that can be disconnected from the load at one time; (2) preventing accidental disconnection of battery strings; (3) a lockout/tagout feature that prevents accidental reconnection during maintenance; (4) allowing a single controller to be removed from the ring without affecting the other controllers; (5) allowing multiple rings to be established within large power systems; and (6) providing an emergency disconnection feature to disconnect all battery strings in an emergency situation when all DC power must be removed.
In accordance with the present invention, a battery control system for controlling the connection of a plurality of batteries to a load is provided. The system comprises a plurality of switches and a plurality of controllers. Each switch is operable to connect or disconnect one of the batteries from the load. Each controller is operatively coupled to one of the switches. Each controller is operative to cause one of the switches to disconnect one of the batteries from the load. Each controller has an input and an output for communicating with other controllers wherein the controllers communicate with each other to limit the number of batteries that can be disconnected from the load.
An UPS system having a plurality of batteries for providing backup power to a load is provided that comprises a plurality of switches and a plurality of controllers. Each switch is operable to connect or disconnect one of the batteries from the load. Each controller is operatively coupled to one of the switches. Each controller is operative to cause one of the switches to disconnect one of the batteries from the load. Each controller has an input and an output for communicating with other controllers wherein the controllers communicate with each other to limit the number of batteries that can be disconnected from the load.
A power plant for providing power to a load is provided. The power plant comprises a source of AC power, an AC to DC power converter for converting the AC power to DC power and for supplying the DC power to the load, and an UPS system for providing backup DC power to the load, the UPS system comprising a plurality of batteries. The power plant further comprises a plurality of switches and a plurality of controllers. Each switch is operable to connect or disconnect one of the batteries from the load. Each controller is operatively coupled to one of the switches. Each controller is operative to cause one of the switches to disconnect one of the batteries from the load. Each controller has an input and an output for communicating with other controllers wherein the controllers communicate with each other to limit the number of batteries that can be disconnected from the load.